title: Bandgap engineering of strained monolayer and bilayer MoS2.
abstract: We report the influence of uniaxial tensile mechanical strain in the range 0-2.2% on the phonon spectra and bandstructures of monolayer and bilayer molybdenum disulfide (MoS2) two-dimensional crystals. First, we employ Raman spectroscopy to observe phonon softening with increased strain, breaking the degeneracy in the E' Raman mode of MoS2, and extract a Grüneisen parameter of ~1.06. Second, using photoluminescence spectroscopy we measure a decrease in the optical band gap of MoS2 that is approximately linear with strain, ~45 meV/% strain for monolayer MoS2 and ~120 meV/% strain for bilayer MoS2. Third, we observe a pronounced strain-induced decrease in the photoluminescence intensity of monolayer MoS2 that is indicative of the direct-to-indirect transition of the character of the optical band gap of this material at applied strain of ~1%. These observations constitute a demonstration of strain engineering the band structure in the emergent class of two-dimensional crystals, transition-metal dichalcogenides.
authors.affiliation: Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee 37235, United States.
authors.forename: Hiram J
authors.initials: HJ
authors.lastname: Conley
authors.forename: Bin
authors.initials: B
authors.lastname: Wang
authors.forename: Jed I
authors.initials: JI
authors.lastname: Ziegler
authors.forename: Richard F
authors.initials: RF
authors.lastname: Haglund
authors.forename: Sokrates T
authors.initials: ST
authors.lastname: Pantelides
authors.forename: Kirill I
authors.initials: KI
authors.lastname: Bolotin